DIAGENETIC CONTROLS ON CARBONATE RESERVOIR QUALITY: A CASE STUDY OF THE SRH WELL, KAIS FORMATION, SALAWATI BASIN, SOUTHWEST PAPUA

Abstract

The Kais Formation carbonate reservoir is the main hydrocarbon-producing rock in the Salawati Basin, Southwest Papua. The reservoir quality of this carbonate reservoir is highly heterogeneous due to post-depositional diagenetic processes. This study assesses the influence of diagenesis on the carbonate reservoir quality in the SRH well by integrating conventional core description, petrographic observations, scanning electron microscopy (SEM), X-ray diffraction (XRD) routine core analysis (RCAL), and petrophysical analysis from well log data. Two carbonate facies were identified, there are bioclastic packstone and bioclastic wackestone, deposited in back-reef lagoon environment. The results of petrographic and SEM observations indicate that dissolution, compaction, replacement, and cementation are diagenetic processes that affect the reservoir quality. Core porosity ranges from 2.51% to 29.65% with an average of 19.74%, while permeability ranges from 0.01 to 257.98 mD with an average of 38.27 mD. Based on petrophysical analysis, the effective porosity (PHIE) values vary from 1.79% to 29.95% with an average of 11.93%. Although porosity values are relatively consistent across several intervals, permeability values show significant variations, indicating that pore connectivity is more strongly controlled by diagenetic processes than pore volume. Dissolution and fracturing enhance reservoir quality through the development of secondary pore systems and increased pore connectivity, while compaction and cementation reduce permeability by decreasing pore connectivity. Replacement associated with micro-intercrystalline carbonate textures may locally maintain or enhance the pore connectivity depending on the extent of recrystallization and cementation. These findings indicate that post-depositional diagenetic processes are the primary controls on carbonate reservoir quality in SRH well and highlight the importance of integrating geological observations, core analyses, and petrophysical data for reliable carbonate reservoir characterization.